Method for producing a continuous length of copper rod from molten copper metal



1967 J. A. BELL ETAL 3,

METHOD FOR PRODUCING A CONTINUOUS LENGTH OF COPPER ROD FROM MOLTEN COPPER METAL Filed Sept. 25, 1964 co'PPEa \MPUEFHES \NVENTORS \J.A.BE\ D.B.COFEQ GESOEBEE BY Q C; M ay ATTOE NEY United States Patent W York Filed Sept, 25, 1964, Ser. No. 399,140 3 Claims. (Cl. 29528) ABSTRACT OF THE DISCLOSURE In a method of continuously casting molten copper into a continuous bar in which the molten copper is refined to the extent necessary to meet the requirements of ASTM designation B-5 and in which the cast bar is immediately hot-rolled into copper rod, the lead content in the molten copper as a metallic impurity is controlled to a level on the order of 0.002% by weight or less, thereby to control the total impurity content of the molten copper to a level such that stress cracking in the continuous bar is substantially eliminated.

This invention relates to a method for producing a continuous length of copper rod from molten copper metal, and more particularly to a method which makes production of a continuous length of copper rod possible through the controlling of the grain structure of a continuous cast copper bar which is produced by and immediately utilized in this method for the production of the copper rod. It is an object of this invention to provide an improved method of such character.

In recent years efforts have been made in the metallurgical field to develop methods and apparatus for continuously producing from molten metal a finished wire rod product. The advantages to be derived from methods of the continuous type are apparent in that a substantial cost savings may be realized from the elimination of such prior art operations as initially casting individual bars of the metal, cooling such bars in the casting molds, .stripping the bars from the casting molds, and subsequently reheating ,such bars to a temperature whereat the bars may be rolled into Wire rod.

One continuous metal processing method, successfully developed and applied to some metals, is the Properzi Process wherein the desired metal, initially introduced into a peripheral groove on a continuously rotating casting wheel in the molten state and allowed to solidify therein, is stripped from the casting Wheel in the form of a cast bar which is immediately introduced into a rolling mill to, produce a continuous length of wire rod product. The method of and apparatus for performing the Properzi Process are fully disclosed and described in the following US. patents to I. Properzi: 2,659,948, Nov. 24, 1953; 2,659,949, Nov. 24, 1953; 2,710,433, June 14, 1955; 2,789,450, Apr. 23, 1957; and 2,865,067, Dec. 28, 1958.

In attempting to apply the Properzi Process to the continuous production of copper Wire rod from molten copper metal difficulties were encountered. In the Properzi Process, or in any other type of continuous process, a certain amount of force is applied to the continuous cast bar to strip the bar from the casting mold. When applied to a cast bar having a grain structure wherein individual copper grains are substantially surrounded by a continuous grain boundary 'network consisting of the Patented Oct. 31, 1967 impurities contained in the molten copper metal, thes forces result in the production of stress cracks along the surface of the bar. In the continuous process, the subsequent rolling of a bar having such stress cracks results in a series of complete ruptures of the bar as it passes through the rolling mill thereby precluding the production of a continuous length of copper wire rod.

Therefore, it is another object of this invention to provide a method for producing a continuous length of copper rod from molten copper metal which insures the uninterrupted production of such a rod.

It is still another object of this invention to provide a method for producing a continuous length of copper rod from molten copper metal, the copper rod so produced having uniform physical properties across a cross section thereof so as to allow a drawing thereof into wire having acceptable electrical conducting characteristics.

It is a further object of this invention to provide a method for producing continuous cast copper rod from molten copper metal which is both simple and reliable in operation and economical to utilize.

With these objects in view, it is a feature of the method of this invention to produce continuous cast copper bar from molten copper metal by controlling the impurity level of a single metallic impurity of the molten copper metal to insure that the grain structure of the continuous copper bar is of such a nature that the bar may be both removed from the continuous casting mold without stress cracking thereof and immediately subjected to a rolling operation to produce a continuous length of copper rod without rupture thereof.

The invention is directed to an improvement of the continuous metal processing techniques which allow adaptations of these techniques to the production of copper rod from molten copper metal. More specifically, the lead content of molten copper metal utilized for production of a continuous length of copper rod is controlled to a level effective to control the total impurity content of the molten copper such that the impurities driven to the grain boundaries during solidification of the molten copper into the cast bar is not sufficient to form a substantially continuous grain boundary network around the copper metal grains in the cast bar. When the cast bar has a grain structure substantially free of a continuous grain boundary network of impurities, the cast bar produced in the casting operation may be subjected to an immediate rolling operation to produce a continuous length of copper rod.

This invention, together with further objects and advantages thereofwill best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view of the apparatus utilized in the Properzi Process for the continuous production of wire rod from molten metal;

FIG. 2 is a representation of a photomicrograph showing a portion of a cast copper bar wherein copper metal grains have a substantially continuous grain boundary of impurities therearound; and

FIG. 3 is a representation of a photomicrograph showing a portion of a cast copper bar wherein individual grains of impurities are included among individual copper grains.

In FIG. 1, a schematic view is shown of apparatus utilized in the Properzi Process for the continuous production of wire rod from molten metal. While the Properzi Process is fully disclosed and described in the above-identified patents to I. Properzi, a brief description thereof will be included herein for the purpose of illustrating the preferred embodiment of the method of this invention.

Copper metal is initially refined in a refining furnace and directed by means of a trough 11 to a delivery device 12 having a nozzle 13 thereon. Molten copper metal is directed through the nozzle 13 and delivered to a peripheral groove on a continuou rotating casting wheel 14. A metal band 16 encircles a portion of the casting wheel 14 and a portion of a wheel 17 such that a continuous casting mold is defined by the groove in the casting wheel 14 and the overlying metal band 16 between the points A and B. Molten copper metal, delivered to the continuous casting mold, is solidified and partially cooled during its movement between the points A and B by utilization of cooling water which flows through the interior of the casting wheel 14.

Beyond the point of departure B of the metal band 16 from the casting wheel 14, a solid cast bar 18 of copper metal is withdrawn from the continuous casting mold at a slight angle, so as not to interfere with the metal band 16, through the cooperation of a stripper element 19 and a driven conveyor 20 which is disclosed and claimed in a copending application of R. Richards, A. M. Wagner, G. C. Ward, Ser. No. 399,145, filed Sept. 25, 1964, and assigned to the same assignees as this application. When the cast bar 18 engages the stripper element 19, the driven conveyor 20 exerts a sufficient amount of force on the cast bar to cause a stripping thereof from the continuous casting mold on the casting wheel 14. Also at point B, the cast bar 18 has been cooled only an amount sufficient to solidify the bar but yet maintain the bar at an elevated temperature to allow an immediate rolling operation to be performed thereon. At this point, the cast bar 18 has a cross-sectional area of several square inches.

The cast bar of copper is immediately directed to a rolling mill 21 and, after passing through several stands of the rolling mill, emerges therefrom as a continuous length of copper wire rod 22 having a substantially uniform circular area of relatively small cross-section. The continuous copper rod 22 is thereafter directed into a coiling basket 23 wherein extremely long lengths of the rod may be accumulated.

In attempting to utilize molten copper metal containing impurities within the limits found acceptable for a prior art process as controlled by ASTM designation B5, difficulty was encountered in that the cast bar 18 tended to develop stress cracks therein as it was withdrawn from the casting wheel 14 by the driven conveyor 20. In subsequent attempts to pass such a stress cracked cast bar through the rolling mill 21, the cast bar completely ruptured at spaced points along its length so as to render production of a continuous length of copper rod impossible.

A significant difference between the prior art process and the continuous process is found in the fact-that in the continuous process the copper bar produced is not cooled to room temperature and subsequently reheated for rolling purposes but rather it is fed directly from the casting device to the rolling mill. In the continuous process, the mechanism of developing the crystal structure of the cast bar is such that the copper metal grains form first, and as these grains form, impurities in the molten copper metal are expelled from the grains to the grain boundaries. If the impurity content of the molten copper is sufliciently high, the impurities expelled during solidification will form a substantially continuous grain boundary network around the copper metal grains as is depicted in FIG. 2. In the prior art process, the cast bar produced is cooled and subsequently slowly reheated such that even though a substantially continuous grain boundary of impurities is formed in the original cast bar, the impurities in the grain boundary agglomerate during reheating thereof to reduce their total exposed area thereby to form a crystal structure such as is depicted in FIG. 3, wherein individual discrete grains of impurities are intermixed with individual discrete grains of copper.

The crystal structure depicted in FIG. 2, which has substantially continuous grain boundaries of impurities, is a relatively weak structure as any stresses applied thereto tend to sever the structure through the substantially continuous grain boundary network. For definition purposes, a cast copper bar has a substantially continuous grain boundary network of impurities when the major portion of a crack through the bar is along impurity copper interfaces.

The crystal structure depicted in FIG. 3, which has an intermixture of copper grains and grains of impurities, is a relatively strong structure as there is no continuous phase through which a crack may find easy passage when the structure is stressed. This particular structure was not subject to stress cracking in the prior art rolling processes and it was felt that if this type of structure could be developed in the cast copper bar produced in the continuous process, the bar so produced would be amenable to an immediate rolling operation without rupture thereof.

To produce a continuous cast copper bar with a grain structure such as depicited in FIG. 3, it was critical that the total impurity content of the molten copper metal be controlled. However, to control the level of each impurity found in the molten copper metal was almost impossible so an attempt was made to try and control the level of a single impurity in the molten copper metal which would be effective, in turn, to directly or indirectly control the total impurity content of the molten metal.

For several reasons it was decided that the content of lead as an impurity in the molten copper metal might prove to be an effective control impurity which would, in turn, control the total impurity content of the molten metal. One reason for considering lead as the control impurity was found in the fact that lead has both a relatively low melting temperature and an extremely low solubility in copper. As such, this element would most assuredly be driven to the grain boundaries during solidification of the molten copper metal into the cast bar. A second reason in considering lead as a possible control impurity was found in the fact that the method utilized for removing lead from molten copper metal does not selectively remove lead alone. Lead is removed by means of a blowing process in which oxygen is introduced directly into the molten copper such that metallic lead is oxidized. This oxidation process is also effective to oxidize other metallic impurities such as tin, iron, silver, etc. Therefore, it appeared that the control of the lead content of the molten copper metal would provide an effective means to control the total impurity content of the molten metal such that the grain structure of a resulting cast copper bar would be one wherein discrete particles of impurities were intermixed with discrete particles of copper.

In order to determine whether lead was an effective control impurity and also at what level it would be effective, various lots of molten copper metal were utilized having differing lead contents therein. In a test procedure samples were taken of the cast bar produced from the various lots of molten copper metal. Such samples, taken from the bar after it left the casting wheel but before it was subjected to a rolling operation, were air cooled to room temperature and a simple test was devised and applied to the samples so taken so as to determine the tendency for any particular sample to stress crack. The test involved bending each of the air cooled samples around a 12 inch diameter pipe and then counting the number of cracks along a one foot section of the sample having the greatest curvature. Cracks were classified as major if they were greater than inch long and minor if visible to the naked eye but less than this length. A short segment of the cast bar was then cut from each sample and subjected to chemical analysis to determine the total lead content thereof. An attempt was also made to produce continuous lengths of copper rod from each lot of molten copper metal and the results thereof recorded for the purpose of correlation,

The following table, showing a representative sample of the results of the testing procedure, records in detail the significant data collected.

From the results of the testing procedure, it was determined that the lead content of the molten copper metal was a control impurity through which the total impurity content of the molten metal could be controlled eifectively. It was further determined that the content of lead in the molten copper metal could not exceed 0.002% by weight of the total metal charge in order that the total impurity content to be controlled to a level such that the grain structure of a cast bar was a mixture of the discrete grains of copper and discrete grains of impurities such as depicited in FIG. 3, the bar having such a structure being amenable to a rolling operation to produce a continuous length of copper rod product.

Therefore, through the control of the impurity level of a single impurity found in molten copper metal, the total impurity content of the molten metal may be controlled such that a continuous length of copper rod may be produced therefrom. However, it should be understood that the chemical analysis of any copper metal intended for use in the continuous process must fall within the ASTM designation B5 although the lead content of such copper must subsequently be reduced to the critical limit by a blowing operation, if necessary. In this regard, it is apparent that if the initial molten copper charge does not meet the critical lead limit and/ or the other requirements of ASTM designation B-S, it may be refined by a blowing process until it does meet both criteria, and that if the charge meets the critical lead limit after having been refined so as to meet the other requirements of ASTM designation B5, further refining to reduce the lead content would not be required.

When the copper metal charge falls within the ASTM designation B-5 and further when the content of lead contained in such a charge has been controlled to the critical level, the cast copper bar produced therefrom in the continuous process will not stress crack during its stripping from the continuous casting wheel. Such a cast bar may be immediately rolled to produce an uninterrupted length of acceptable copper rod which will have uniform physical properties across a cross section thereof so as to allow a drawing thereof into wire having acceptable electrical conducting characteristics. The continuous process, by use of the control features of this invention, is adaptable to the production of a continuous length of copper rod from molten copper metal, the process being simple and reliable in operation and economical to utilize.

While the method of this invention has been disclosed in a preferred embodiment, it is understood that many modifications thereof will be apparent. It is intended that the method of this invention be interpreted as including all modifications which fall within the true spirit and scope thereof.

What is claimed is:

1. In the method of continuously casting molten copper metal into a cast bar and rolling the bar into wire rod wherein the molten copper metal is refined to the extent necessary to make the molten copper substantially meet the requirements of ASTM designation B-S, wherein the molten copper metal is introduced into a continuous casting mold and solidified therein to form a cast bar, wherein the cast bar is withdrawn from the continuous casting mold in a heated condition, and wherein the withdrawn cast bar is immediately subjected to a rolling operation to produce copper wire rod, the improvement which comprises:

controlling the content of lead as a metallic impurity in the molten copper metal to a level effective to control the total impurity content of the molten copper such that the impurities driven to the grain boundaries during solidification of the molten copper into the cast bar are not sufiicient to form a substantially continuous grain boundary network around the copper metal grains in the cast bar. 2. In the method of continuously casting molten copper metal into a cast bar and rolling the bar into wire rod wherein the molten copper metal is refined to the extent necessary to make the molten copper substantially meet the requirements of ASTM designation B-S, wherein the molten copper metal is introduced into a continuous casting mold and solidified therein to form a cast bar, wherein the cast bar is withdrawn from the continuous casting mold in a heated condition, and wherein the withdrawn cast bar is immediately subjected to a rolling operation to produce copper wire rod, the improvement which comprises:

controlling the content of lead as a metallic impurity in the molten copper metal to a level not substantially in excess of 0.002% by weight of the total molten metal thereby to control the total impurity content of the molten copper such that the impurities driven to the grain boundaries during solidification of the molten copper into the cast bar are not sufiicient to form a substantially continuous grain boundary network around the copper metal grains in the cast bar. 3. In the method of continuously casting molten copper metal into a cast bar and rolling the bar into wire rod wherein the molten copper metal is refined to the extent necessary to make the molten copper substantially meet the requirements of ASTM designation B5, wherein the molten copper metal is introduced into a continuous casting mold and solidified therein to form a cast bar, where in the cast bar is withdrawn from the continuous casting mold in a heated condition, and wherein the withdrawn cast bar is immediately subjected to a rolling operation to produce copper wire rod, the improvement which comprises:

controlling the content of lead as a metallic impurity in the molten copper metal to a level of 0.002% by weight or less of the total molten metal thereby to control the total impurity content of the molten copper such that the impurities driven to the grain boundaries during solidification of the molten copper into the cast bar are not sufiicient to form a substantially continuous grain boundary network around the copper metal grains in the cast bar.

References Cited UNITED STATES PATENTS 2,710,433 6/1955 Properzi 22200.1 3,258,330 6/1966 Ito --76 FOREIGN PATENTS 465,122 4/1937 Great Britain.

CHARLIE T. MOON, Primary Examiner.

R. F. DROPKIN, Assistant Examiner. 

1. IN THE METHOD OF CONTINUOUSLY CASTING MOLTEN COPPER METAL INTO A CAST BAR AND ROLLING THE BAR INTO WIRE ROD WHEREIN THE MOLTEN COPPER METAL IS REFINED TO THE EXTENT NECESSARY TO MAKE THE MOLTEN COPPER SUBSTANTIALLY MEET THE REQUIREMENTS OF ASTM DESIGNATION B-5, WHEREIN THE MOLTEN COPPER METAL IS INTRODUCED INTO A CONTINUOUS CASTING MOLD AND SOLIDIFIED THEREIN TO FORM A CAST BAR, WHEREIN THE CAST BAR IS WITHDRAWN FROM THE CONTINUOUS CASTING MOLD IN A HEATED CONDITION, AND WHEREIN THE WITHDRAWN CAST BAR IS IMMEDIATELY SUBJECTED TO A ROLLING OPERATION TO PRODUCE COPPER WIRE ROD, THE IMPROVEMENT WHICH COMPRISES: 